The invention relates to a turbine housing of an exhaust gas turbocharger with a variable turbine geometry.
Exhaust gas turbochargers, in the case of which the supercharging pressure can be controlled by means of adjustable vanes, are known, for example, from German Patent Document DE 103 12 324 B3. In the turbine housing of such VTG (variable turbine geometry) chargers, a vane apparatus is fastened which consists of a support ring for the vanes, as well as a covering ring which is situated opposite the support ring while maintaining a vane gap distance. For the spacing of the support ring and the covering ring, spacing elements, for example, in the form of spacing sleeves, are provided which are arranged to be radially distributed around the circumference of both rings, which spacing elements are held or penetrated by corresponding fastening elements, for example, in the form of fastening screws. Particularly when these VTG chargers are used in the case of Otto engines, these components are exposed to high exhaust gas temperatures. In this case, the spacing elements, which are penetrated by the holding elements, are particularly critical. When the spacing elements are acted upon by a hot exhaust gas flow, they correspondingly expand in the longitudinal direction, while the holding elements are still relatively cold. This may lead to an unacceptable linear expansion of the holding elements beyond their yielding point. Conversely, in the event of a subsequent load jump (full load to lower partial load), first the spacing element is cooled by the exhaust gas flow while the holding element is still relatively hot. This leads to a faster shrinking of the spacing element with respect to the holding element. If the holding element is constructed as a fastening screw, this results in a loss of prestressing force. As a result of loss of prestressing force, the fastening screw now has to absorb all transverse forces occurring because of the engine operation, which, under certain circumstances, may lead to component failure of the fastening screw.
It is an object of the invention to overcome the above-described disadvantages so that a reliable continuous operation of the VTG charger is guarantied.
As a result of recesses provided in the spacing elements, it is ensured that also the holding element is directly acted upon by the exhaust gas mass flow. While the material characteristics are the same or similar, this leads to a uniform expansion or shrinkage behavior of both components, so that a durable fastening is guarantied.
The characteristics indicated below allow additional developments and further developments of the turbine housing or of the vane apparatus for a VTG charger.
The recesses, which permit a direct action upon the holding elements by means of the exhaust gas flow, are advantageously placed in the generated surface of the spacing elements.
In this case, the recesses are constructed in a simple manner as bores, for example, four bores, which are each placed radially offset by 90 degrees with respect to one another in the generated surface.
As a second embodiment, the recesses are constructed as slots which are made from the direction of the face of the spacing elements.
Recesses, in which the spacing elements engage with their faces in a form-locking manner, are provided in the support and covering ring. This results in a fit by way of which transverse forces are absorbed, so that the holding elements are essentially free of transverse forces at this point.
Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.